Standard deviation?

[margrades]

What is standard deviation and how is used in defining a player? What other important formulas should i consider while at poker table?

[alphatmw]

square root of variance
it isn't
wtf formulas?

[jay_shark]

Var(x) = (x-mean)^2/n{sum over all x's}
n=number of elements in your sample .

ie 1,3,6,7,9 n=5

mean = 5.2 which is the average of all the numbers.

x1=1,x2=3,x3=6,x4=7,x5=9

Therefore
[(1-5.2)^2+(3-5.2)^2 +(6-5.2)^2+(7-5.2)^2+(9-5.2)^2]/5 =var

Now st(x)= sqrt of the number computed above .

or even better use var(x)=x^2{sum over all x's} - mean ^2

When n is sufficiently large , over 30 , the standard deviation can tell you how close your data is from the mean .

ie 1 standard deviation from the mean contains 68 % of the data

2 standard deviations contains around 95 % of the data .

[sandman-54]

Standard deviation (per hour) is a statistical measure of dispertion of data (hours or n from above). Standard deviation measures the so-called "swings" of the game in a definite, rather than relative, way. Almost all results will be within 3 standard deviations of the arithmetic mean (winrate per hour).

The most important way to define a player when considering the standard deviation is the relationship between the winrate, or possibly game size, and standard deviation.

Consider two experts of the same skill. If one either has a smaller bankroll or less of a willingness to live a volatile financial life, he may choose to avoid marginally correct plays. In so doing, he will lower his winrate for sure, but lower his standard deviation both in a definite and relative sense.

I love twoplustwo poker texts!